Nowadays, radio frequency switching circuits or RF switching circuits are implemented in many electronic apparatuses and utilized, for example, as clock generators or basic frequency generators for receiving and/or transmitting units for data transfer by radio. Respective radio frequency switching circuits are employed both in mobile apparatuses and in apparatuses, which tend to be used in the non-mobile field. Examples of respective mobile apparatuses are portable minicomputers such as PDAs (PDA=personal data assistant) or cell phones.
Frequently, fully integrated phase-locked circuits or PLL circuits (PLL=phase-locked loop) are realized in the respective RF switching circuits. Often, the core of such a phase-locked circuit is a voltage-controlled oscillator or VCO, which is dimensioned such that it tolerates scatterings regarding the frequency, which may occur, for example, as a result of productional and/or operational parameters (temperature variations or variations in the supply voltage), and still constantly generates the desired frequency. Next to balancing the scattering due to production, temperature and supply voltage, the VCO or the corresponding RF switching circuit must also often cope with various frequency bands, which is why an integrated VCO must generally be controllable across a large frequency range. Therefore, the VCO tolerates these scatterings and is capable of balancing the (current) frequency such, with the aid of adjustable components (tuning components), that in the end it will generate the correct frequency.
With voltage-controlled oscillators covering a large frequency and temperature range, it is therefore advisable to pay particular attention to an amplitude of an oscillation provided by the voltage-controlled oscillator (output amplitude) as same basically largely depends on the respective operating conditions. In order to ensure safe functioning of the overall circuit it is therefore generally necessary that the output amplitude or amplitude be large enough to be able to drive subsequent circuits. At the same time, in a corresponding design of the respective RF switching circuit, it must be taken into consideration that often only a limited amount of energy is available for the operation of the respective IC (IC=integrated circuit). This particularly applies to mobile applications, in which battery-powered or accumulator-powered ICs are often employed. In order to maximize the battery or accumulator lifetime, it is therefore advisable to provide a minimum amount of current for the operation of the respective RF switching circuit, which may lead to significant limitation of the specified parameters of the RF switching circuit.